In June, Duolingo introduced its model for combining language learning with translating Web pages and documents into a variety of languages. The startup developed a free, "gamified" application that lets users acquire languages (English, Spanish, French, German and Portuguese are supported currently) by progressing though a set of skill exercises, with virtual rewards to make the learning experience more engaging and effective.

Embedded in the game mechanics are exercises that ask users to translate part of documents and web pages. These translations underlie Duolingo's crowdsourcing business model, which charges customers for the translations delivered by the language students. Duolingo compares translations from the pool of people using the service to derive more accuracy. For starters, the company is working with news organizations to employ the crowdsourced translation service, said CEO Luis von Ahn.

When Duolingo was introduced earlier this year, von Ahn said his goal was to attract 100 million people to the language-learning service. So far, Duolingo has attracted 300,000 active users, who use the site for an average of 30 minutes per day, according to von Ahn. A Duolingo iPhone app has just been released, and an Android version is expected next year. "We get a lot of requests for iPhone and Android apps, so we're hoping it will have a major impact," he said.

English is the most popular language to learn, accounting for more than 50 percent of the usage, said von Ahn, followed by Spanish, and then French, German, Portuguese. About 25 percent of Duolingo users are based in the U.S., followed by 13 percent in Brazil and 10 percent in Mexico and Spain.

Von Ahr said he doesn't expect the company to start generating revenue until next year, but with $18.3 million raised from venture firms Union Square Ventures, NEA, and A-Grade Investments, he can afford to invest in building out the service. Chinese and Japanese languages are expected to be added to Duolingo's curriculum next year.